Since small vessel emboli (e.g., intracranial clots) are usually difficult to remove mechanically due to the limited size of the vessel, catheter-directed fibrinolysis is frequently considered to be the best available treatment. The goal associated with catheter-directed fibrinolysis is to deliver a fibrinolytic agent directly to a thrombus in order to activate the plasminogen bound to the fibrin clot. In order to achieve this goal, an infusion catheter or wire is typically embedded within the thrombus and a fibrinolytic agent, such as a tissue-type plasminogen activator (t-PA), is continuously infused through the catheter at a rate of 1-2 mg per hour until successful dissolution of the thrombus is achieved between 12-18 hours later.
One problem routinely encountered during such catheter-directed fibrinolysis is pericatheter thrombosis. Pericatheter thrombosis results from poor blood flow along the length of the catheter. In order to decrease the incidence of this problem, a low dosage of intraveneous heparin (500-1000 units/hr) is frequently introduced into the vessel through the catheter's sheath. Anticoagulation with heparin is also known to be helpful to prevent rebound thrombosis after the fibrinolytic infusion is completed. Additional methods used to reduce the occurrence of pericatheter thrombosis is to keep the intravascular length of catheter to a minimum, to use a catheter with the smallest possible diameter, and to reduce the overall length of time associated with the infusion.
An additional complication that can be encountered during catheter-directed fibrinolysis is related to the occurrence of bleeding at the arterial puncture site. This type of complication is usually considered minor, but can be life threatening if it occurs at a remote site (i.e., intracranial, etc.). The risk associated with the occurrence of this complication is known to increase with the length of time associated with the infusion.
Accordingly, there exists a need to reduce the risks associated with catheter-directed fibrinolysis in small vessels. In particular, there exists a need to deliver the necessary dosage of fibrinolytic agent to achieve complete dissolution of the emboli over the shortest duration of time, while maintaining the minimum necessary diameter and length for the catheter used for the infusion.